Post-traumatic stress disorder (PTSD) represents a debilitating psychiatric condition that is affecting the lives of many returning OEF/OIF veterans. PTSD and alcohol use disorders are highly comorbid. As many as 50- 85% of individuals with PTSD have a comorbid alcohol use disorder (Kessler et al., 1995). This association is commonly attributed to individuals using alcohol to self-medicate (Stewart, 1997). However, the precise functional associations between PTSD symptoms and alcohol disorder are not well understood. For example, there is some evidence that PTSD may be associated with decreased self-control, which in turn increases alcohol-related problems (Miller et al., 2006). In addition, characteristics such as impulsivity and emotional intelligence may act as vulnerability or resilience factors, moderating associations between symptoms and alcohol outcomes (Simons et al., 2005;Austin, Saklofske, Egan, 2005;Riley &Shutte, 2003;Brackett, Mayer &Warner, 2004). Previous research has relied primarily on surveys to examine between-person differences. Examining both between- and within- person associations by repeated assessments of behavior in near real time can improve knowledge of functional mechanisms underlying associations between PTSD symptoms and alcohol use disorder. The proposed 2-week experience sampling study of OEF/OIF veterans examines between- and within- person mechanisms that underlie associations between PTSD symptoms and alcohol consumption and problems. (1) Baseline PTSD symptoms are hypothesized to be associated with increased rates of alcohol consumption and problems and these associations are hypothesized to be mediated by increased negative affectivity and negative urgency (i.e., impulsivity). Previous research has identified negative affectivity and impulsivity as mediators at the between-subject level (Miller et al., 2006). The proposed study examines the mediation role of negative affectivity at both the between- and within- person levels. Also, the proposed study will examine a specific aspect of impulsivity, negative urgency (2) There will be positive associations between daily variability of PTSD symptoms and negative affect and subsequent nighttime drinking and problems. Significance of the semi-partial regression coefficients will determine whether PTSD symptoms are associated with alcohol behaviors when controlling for negative affect. Previous research has identified significant prospective associations between PTSD symptoms and negative affect and alcohol problems (Miller et al., 2006). The proposed study extends this research to examine these associations at the event level to precisely examine the functional association. That is, how do PTSD symptoms and alcohol problems covary on a day-to-day basis? Finally, the proposed study examines protective and vulnerability factors. (3) Emotional intelligence will attenuate, and negative urgency increase, the within-person associations between PTSD symptoms and negative affect and subsequent alcohol use and problems. These hypotheses will be examined by testing cross-level interactions. PUBLIC HEALTH RELEVANCE: This research uses innovative methodology to explore the relationships among traumatic symptoms, vulnerability (impulsivity) and resilience factors (emotional intelligence), and alcohol use and problems among recent returning veterans. This research tests a novel approach to assessing traumatic stress symptoms and associated problems and aims to examine mechanisms underlying these difficulties that may be addressed in treatment. It is also hoped that the results will stimulate future use of portable computer technology in traumatic stress research to better understand the problems and strengths of returning veterans.